| Message ID | 20231027083558.484911-1-roberto.sassu@huaweicloud.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | security: Move IMA and EVM to the LSM infrastructure | expand |
On Fri, 2023-10-27 at 10:35 +0200, Roberto Sassu wrote: > From: Roberto Sassu <roberto.sassu@huawei.com> > > IMA and EVM are not effectively LSMs, especially due to the fact that in > the past they could not provide a security blob while there is another LSM > active. > > That changed in the recent years, the LSM stacking feature now makes it > possible to stack together multiple LSMs, and allows them to provide a > security blob for most kernel objects. While the LSM stacking feature has > some limitations being worked out, it is already suitable to make IMA and > EVM as LSMs. > > In short, while this patch set is big, it does not make any functional > change to IMA and EVM. IMA and EVM functions are called by the LSM > infrastructure in the same places as before (except ima_post_path_mknod()), > rather being hardcoded calls, and the inode metadata pointer is directly > stored in the inode security blob rather than in a separate rbtree. > > To avoid functional changes, it was necessary to keep the 'integrity' LSM > in addition to the newly introduced 'ima' and 'evm' LSMs, despite there is > no LSM ID assigned to it. There are two reasons: first, IMA and EVM still > share the same inode metadata, and thus cannot directly reserve space in > the security blob for it; second, someone needs to initialize 'ima' and > 'evm' exactly in this order, as the LSM infrastructure cannot guarantee > that. > > The patch set is organized as follows. > > Patches 1-9 make IMA and EVM functions suitable to be registered to the LSM > infrastructure, by aligning function parameters. > > Patches 10-18 add new LSM hooks in the same places where IMA and EVM > functions are called, if there is no LSM hook already. > > Patches 19-22 do the bulk of the work, introduce the new LSMs 'ima' and > 'evm', and move hardcoded calls to IMA, EVM and integrity functions to > those LSMs. In addition, they reserve one slot for the 'evm' LSM to supply > an xattr with the inode_init_security hook. > > Finally, patch 23 removes the rbtree used to bind integrity metadata to the > inodes, and instead reserves a space in the inode security blob to store > the pointer to that metadata. This also brings performance improvements due > to retrieving metadata in constant time, as opposed to logarithmic. > > The patch set applies on top of lsm/next-queue, commit 0310640b00d2 ("lsm: > don't yet account for IMA in LSM_CONFIG_COUNT calculation"), plus commits > in linux-integrity/next-integrity-testing up to bc4532e9cd3b ("ima: detect > changes to the backing overlay file"). Thanks, Roberto! The patch set looks really good. I just sent a few very minor comments. Mimi
From: Roberto Sassu <roberto.sassu@huawei.com> IMA and EVM are not effectively LSMs, especially due to the fact that in the past they could not provide a security blob while there is another LSM active. That changed in the recent years, the LSM stacking feature now makes it possible to stack together multiple LSMs, and allows them to provide a security blob for most kernel objects. While the LSM stacking feature has some limitations being worked out, it is already suitable to make IMA and EVM as LSMs. In short, while this patch set is big, it does not make any functional change to IMA and EVM. IMA and EVM functions are called by the LSM infrastructure in the same places as before (except ima_post_path_mknod()), rather being hardcoded calls, and the inode metadata pointer is directly stored in the inode security blob rather than in a separate rbtree. To avoid functional changes, it was necessary to keep the 'integrity' LSM in addition to the newly introduced 'ima' and 'evm' LSMs, despite there is no LSM ID assigned to it. There are two reasons: first, IMA and EVM still share the same inode metadata, and thus cannot directly reserve space in the security blob for it; second, someone needs to initialize 'ima' and 'evm' exactly in this order, as the LSM infrastructure cannot guarantee that. The patch set is organized as follows. Patches 1-9 make IMA and EVM functions suitable to be registered to the LSM infrastructure, by aligning function parameters. Patches 10-18 add new LSM hooks in the same places where IMA and EVM functions are called, if there is no LSM hook already. Patches 19-22 do the bulk of the work, introduce the new LSMs 'ima' and 'evm', and move hardcoded calls to IMA, EVM and integrity functions to those LSMs. In addition, they reserve one slot for the 'evm' LSM to supply an xattr with the inode_init_security hook. Finally, patch 23 removes the rbtree used to bind integrity metadata to the inodes, and instead reserves a space in the inode security blob to store the pointer to that metadata. This also brings performance improvements due to retrieving metadata in constant time, as opposed to logarithmic. The patch set applies on top of lsm/next-queue, commit 0310640b00d2 ("lsm: don't yet account for IMA in LSM_CONFIG_COUNT calculation"), plus commits in linux-integrity/next-integrity-testing up to bc4532e9cd3b ("ima: detect changes to the backing overlay file"). Changelog: v3: - Drop 'ima: Align ima_post_path_mknod() definition with LSM infrastructure' and 'ima: Align ima_post_create_tmpfile() definition with LSM infrastructure', define the new LSM hooks with the same IMA parameters instead (suggested by Mimi) - Do IS_PRIVATE() check in security_path_post_mknod() and security_inode_post_create_tmpfile() on the new inode rather than the parent directory (in the post method it is available) - Don't export ima_file_check() (suggested by Stefan) - Remove redundant check of file mode in ima_post_path_mknod() (suggested by Mimi) - Mention that ima_post_path_mknod() is now conditionally invoked when CONFIG_SECURITY_PATH=y (suggested by Mimi) - Mention when a LSM hook will be introduced in the IMA/EVM alignment patches (suggested by Mimi) - Simplify the commit messages when introducing a new LSM hook - Still keep the 'extern' in the function declaration, until the declaration is removed (suggested by Mimi) - Improve documentation of security_file_pre_free() - Register 'ima' and 'evm' as standalone LSMs (suggested by Paul) - Initialize the 'ima' and 'evm' LSMs from 'integrity', to keep the original ordering of IMA and EVM functions as when they were hardcoded - Return the IMA and EVM LSM IDs to 'integrity' for registration of the integrity-specific hooks - Reserve an xattr slot from the 'evm' LSM instead of 'integrity' - Pass the LSM ID to init_ima_appraise_lsm() v2: - Add description for newly introduced LSM hooks (suggested by Casey) - Clarify in the description of security_file_pre_free() that actions can be performed while the file is still open v1: - Drop 'evm: Complete description of evm_inode_setattr()', 'fs: Fix description of vfs_tmpfile()' and 'security: Introduce LSM_ORDER_LAST', they were sent separately (suggested by Christian Brauner) - Replace dentry with file descriptor parameter for security_inode_post_create_tmpfile() - Introduce mode_stripped and pass it as mode argument to security_path_mknod() and security_path_post_mknod() - Use goto in do_mknodat() and __vfs_removexattr_locked() (suggested by Mimi) - Replace __lsm_ro_after_init with __ro_after_init - Modify short description of security_inode_post_create_tmpfile() and security_inode_post_set_acl() (suggested by Stefan) - Move security_inode_post_setattr() just after security_inode_setattr() (suggested by Mimi) - Modify short description of security_key_post_create_or_update() (suggested by Mimi) - Add back exported functions ima_file_check() and evm_inode_init_security() respectively to ima.h and evm.h (reported by kernel robot) - Remove extern from prototype declarations and fix style issues - Remove unnecessary include of linux/lsm_hooks.h in ima_main.c and ima_appraise.c Roberto Sassu (23): ima: Align ima_inode_post_setattr() definition with LSM infrastructure ima: Align ima_file_mprotect() definition with LSM infrastructure ima: Align ima_inode_setxattr() definition with LSM infrastructure ima: Align ima_inode_removexattr() definition with LSM infrastructure ima: Align ima_post_read_file() definition with LSM infrastructure evm: Align evm_inode_post_setattr() definition with LSM infrastructure evm: Align evm_inode_setxattr() definition with LSM infrastructure evm: Align evm_inode_post_setxattr() definition with LSM infrastructure security: Align inode_setattr hook definition with EVM security: Introduce inode_post_setattr hook security: Introduce inode_post_removexattr hook security: Introduce file_post_open hook security: Introduce file_pre_free_security hook security: Introduce path_post_mknod hook security: Introduce inode_post_create_tmpfile hook security: Introduce inode_post_set_acl hook security: Introduce inode_post_remove_acl hook security: Introduce key_post_create_or_update hook ima: Move to LSM infrastructure ima: Move IMA-Appraisal to LSM infrastructure evm: Move to LSM infrastructure integrity: Move integrity functions to the LSM infrastructure integrity: Switch from rbtree to LSM-managed blob for integrity_iint_cache fs/attr.c | 5 +- fs/file_table.c | 3 +- fs/namei.c | 12 +- fs/nfsd/vfs.c | 3 +- fs/open.c | 1 - fs/posix_acl.c | 5 +- fs/xattr.c | 9 +- include/linux/evm.h | 103 ---------- include/linux/ima.h | 142 -------------- include/linux/integrity.h | 26 --- include/linux/lsm_hook_defs.h | 20 +- include/linux/security.h | 59 ++++++ include/uapi/linux/lsm.h | 2 + security/integrity/evm/evm_main.c | 138 ++++++++++++-- security/integrity/iint.c | 113 +++++------ security/integrity/ima/ima.h | 11 ++ security/integrity/ima/ima_appraise.c | 37 +++- security/integrity/ima/ima_main.c | 96 ++++++++-- security/integrity/integrity.h | 58 +++++- security/keys/key.c | 10 +- security/security.c | 261 ++++++++++++++++---------- security/selinux/hooks.c | 3 +- security/smack/smack_lsm.c | 4 +- 23 files changed, 614 insertions(+), 507 deletions(-)